The present invention relates, in general, to wind electric plants, and more particularly, to a wind electric plant of the type which includes a wind driven propeller or the like to drive an alternator for producing electrical energy as disclosed in applicants' U.S. Pat. No. 4,059,771, issued Nov. 22, 1977.
The above-referenced patent and applicants' co-pending application for Letters Patent Ser. No. 887,373, filed Mar. 16, 1978, disclose battery controlled variable speed alternator systems for wind electric operation wherein battery current is utilized as the source of excitation current for the field winding of the alternator which battery current controls the excitation of the alternator field to provide a relatively constant excitation current for the alternator field winding, whereby the alternator field is fully excited at substantially all speeds of operation thereof.
In U.S. Pat. No. 4,059,771, alternator output is controlled directly through controls responsive to alternator speed and battery voltage to provide a relatively constant excitation current for the field winding of the alternator from a storage battery, wherein battery current is directly applied to the alternator field and whereby the alternator field is fully excited at substantially all speeds of operation thereof.
In applicants' above-referenced co-pending application, an improvement of U.S. Pat. No. 4,059,771 is disclosed wherein alternator output is controlled indirectly through the field control of an exciter and battery current is utilized to provide the excitation current for the exciter field winding which thereby, via an associated exciter armature, controls the excitation of the alternator field winding. Associated circuitry is also provided so that power can be alternatively supplied to either hot water heater loads or to auxiliary loads, at least one of which is solar-powered, thereby maintaining a full or constant load on the wind electric power plant to ensure the quiet operation of that plant even at times of strong wind conditions.
In the present improvement, alternator output is controlled through the use of an exciter including an exciter armature and an associated permanent magnet exciter field which eliminates the use of battery current as the source of excitation current for the field winding of the alternator and which thereby eliminates the need for the more expensive solid-state battery current control system required in applicants' herein-referenced U.S. patent and co-pending application.
As disclosed in the above-referenced co-pending application, the inventors have found that the field of wind electric plants has need of means for energizing the field of an alternator so that the alternator can develop full voltage at slow speed while also permitting speed increases of two or three times the starting speed. Such means should also permit full control of the energy output of the overall device. The present improvement further satisfies this need by providing a wind electric plant which increases the efficiency of the alternator while at the same time advantageously providing a much less costly wind electric generation plant of the type described.
The inventors have noted that during the operation of a wind electric plant of the type described in U.S. Pat. No. 4,059,771 and, more specifically, during operation of a variable pitch speed controlled propeller device, there is considerable "on and off" pressure strain applied to the propeller area from the wind as a governor device, associated with the wind electric plant operates to change the pitch or blade angle of the propellers to keep them from overspeeding when the load is removed from the alternator. This "on and off" pressure against the propeller blades, caused by the rapid change in pitch of the propellers when the load on the alternator is removed, creates a considerable fluctuating pressure against the propellers, which is also applied against the wind electric plant and its supporting tower structure causing the tower to move back and forth to a considerable degree. This action places considerable strain on the tower and is repeated frequently when the alternator controls remove the load from the alternator. Also, frequent operation of the governor device causes considerable wearing of the governors' control parts.
Furthermore, the fluctuating pressure against the propellers, which is caused by the action of the governor device, causes the wind electric plant located at the top of the tower to sway. Since the wind electric plant has considerable weight, the swaying of that plant causes strain of and possible damage to the tower structure. As the wind pressure against the propellers reduces at the time when they "feather", the strain on these propellers is, accordingly, reduced greatly. Then as the governor device acts to change the pitch of the propellers, the pitch of these propellers being flattened to the wind, this action applies a considerable increase in wind pressure thereto. The action of the governor device causing the beforementioned fluctuating pressure on the propellers, which results in causing the tower structure to sway back and forth, is quite disadvantageous for the following reasons.
The inventors have noted that the sudden swaying of the tower, occurring when the governor device changes the pitch of the propeller blades, may cause the entire wind electric plant and its supporting tower structure to "spring back" or sway several inches. This movement places considerable strain on the propellers and their hub mounts as the propellers shift their operating plane in accordance with the action of the governor device.
The inventors have further noted that when large propellers are utilized such as those having a 20 foot diameter or larger, these propellers have nearly 1500 pounds of "centrifugal" weight in each blade during full speed operation and this "centrifugal" weight travels at a speed of over 100 miles-per-hour while the propellers operate in their revolving plane which is in line with their hub position. When the increased wind pressure is suddenly applied to the propeller diameter due to the action of the governor, the hub is pushed back, along with the wind electric plant and the tower structure, shifting the operating plane of the propellers and causing them to be "sprung" out of their revolving plane until they can shift their considerable "centrifugal" weight to a new position. These beforementioned actions create considerable strain and vibration which may cause damage to the entire wind electric plant system including the propeller blades, the tower structure and other parts of the tower. Furthermore, the resulting strain and vibration also causes jerking and shaking of the tail vane and other mounting and tower parts.
Accordingly, when the propellers are traveling at a high rate of speed and the propellers are forced to change their pitch or operating angle to the wind via the action of a governor device, when the load is removed from the alternator, considerable noise is created by the propellers due to the fact that they no longer present an airfoil contour to air movement past the propellers. This air movement past the propellers may exceed 100 M.P.H. tip speed even though the speed of the wind driving the propellers may only be 12 to 15 M.P.H. when there is no lead on the alternator.
Therefore, the field of wind electric plants has need of means for keeping a constant or full load on the wind electric plant in order to keep the propellers loaded. The present improvement satisfies that need by providing means to keep a constant load on the wind electric plant thereby ensuring quiet operation of that plant.